<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .panel {
      width: 400px;
      height: 400px;
      background: #bababb;
      position: relative;
    }
    .item {
      width: 100px;
      height: 100px;
    }
    .blue {
      background: blue;
      float: left;
      /* opacity: 0.9; */
    }
    .inner {
      width: 80px;
      height: 80px;
      background: green;
    }
    .red {
      background: red;
      display: inline-block;
      margin-left: -50px;
    }
  </style>
</head>
<body>
  <div class="panel">
    <div class="item red"></div>
    <div class="item blue">
      <div class="inner"></div>
    </div>
  </div>
</body>
</html>